In recent years, a fuel cell system in which a fuel cell and hydrogen absorbing alloys are combined has been used as a portable power source. Various constitutions of such a fuel cell system have been proposed (such as Japanese Patent Application Laid-Open Nos. 6-76848 and 6-60894).
Among these, as a typical conventional example, a constitution described in Japanese Patent Application Laid-Open No. 6-150955 will be described in detail referring to FIGS. 9 and 10.
In these drawings, cylinders 32 filled with hydrogen absorbing alloys which supply hydrogen to a fuel cell 31 are contained in a housing 34 of a portable structure independent from a power source body 33 containing the fuel cell 31, and in this housing 34, exhaust gas introducing section 35 is provided so that exhaust gas produced by the fuel cell 31 passes around the cylinders 32.
In this example, since the housing 34 containing the cylinders 32 has a portable structure independent from a power source body 33, the size of the housing 34 can be increased without spatial limitation for the cylinders 32. Also, in order to supply hydrogen smoothly, exhaust gas from the fuel cell 31 is introduced around the cylinders 32 so as to increase the temperature and pressure of the tank.
As the second example, as Japanese Patent Application Laid-Open No. 4-181659 describes, there was a fuel cell system in which the equilibrium hydrogen pressure at the upper limit of the plateau region of hydrogen absorbing alloys as a hydrogen storage means is 10 atm or below under an ordinary pressure, in order to enhance the safety of fuel cell systems.
Incidentally, in conventional fuel cell systems, since the type which operates at a relatively high temperature of 170.degree. C. or above, such as a phosphoric acid type fuel cell, is used as the fuel cell body, cylinders were effectively heated by exhaust gas.
However, when a polymeric electrolyte type fuel cell operating at about 60.degree. C. was used for further reducing the size of fuel cells for the use of electric appliances such as personal computers, and for generating electric power for a long period of time, there was a problem that heating by exhaust gas was difficult.
Furthermore, if the temperature of a hydrogen storage vessel in operation was not an ordinary temperature, and if the equilibrium hydrogen pressure at the upper limit of the plateau region of hydrogen absorbing alloys is 10 atm or below under an ordinary pressure, there was problems that the equilibrium hydrogen pressure in operation elevated when the temperature was higher than the normal temperature, and that the equilibrium hydrogen pressure in operation lowered when the temperature was lower than the normal temperature and that hydrogen can not be supplied.